Although I agree that Tien should be added, I think other characters should be added too. My idea is that essential characters are selectable by default, but a console command could be invented to "unlock" or enable secondary characters such as Vegetto, Gogeta, Androids #13, 16, 17, etc.
ESF is GREAT, but it'd be even better if the DBZ environment could be further enriched by adding more characters. I hope the ESF team adds as many characters as possible.
I also think that, if people are worreid about too many characters, that a command should be created to enable them, so they're not selectable by default.